ASTROCYTIC CALCIUM DYNAMICS DURING HIPPOCAMPAL SHARP-WAVE RIPPLES

Memory consolidation, the process by which newly acquired information is stabilized for long-term storage, relies on hippocampal sharp wave ripples (SWRs). SWRs are brief episodes of neuronal activity characterized by CA1 pyramidal dendrite depolarization (sharp waves) and the simultaneous occurrence of high-frequency oscillations (ripples). While the neuronal basis of SWRs has been extensively studied, the contribution of astrocytes to these events remains unexplored. We combined simultaneous two-photon imaging of astrocytic Ca²⁺ signals with multi-electrode array (MEA) recordings in mouse hippocampus to test whether and how astrocytes participate in SWR generation and maintenance. We uncovered a bidirectional coupling between astrocytes and SWRs. First, astrocytes support SWR emergence: mice lacking IP₃ receptor–mediated Ca²⁺ release in astrocytes displayed significantly fewer and shorter SWRs. Second, SWRs feed back onto astrocytes: astrocytic somatic Ca²⁺ events were transiently decreased immediately after SWRs. To determine the specificity of Ca²⁺ events properties and dynamic modulation during SWRs, we performed similar simultaneous recordings during gamma (γ) oscillations and found distinct astrocytic Ca²⁺ features and dynamics compared with SWR epochs, indicating oscillation-type–specific astrocyte signaling. Together, our findings reveal an active, context-dependent astrocyte–neuron dialogue in the hippocampus and identify astrocytic IP₃-dependent Ca²⁺ signaling as a determinant of SWR occurrence. Our findings thus position astrocytes as modulators, not merely bystanders of the network patterns thought to underlie memory consolidation.